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Organization of the Body and Body Tissues
Up Course Syllabus Basic Chemical and Cellular Biology Organization of the Body and Body Tissues Integumentary System;Bones and Skeletal Tissue The Skeleton and Joints The Muscular System Cardiovascular System: Blood Cardiovascular System: The Heart Cardiovascular System: Blood Vessels Test Scores/Final Grades Practical exams



Anatomy and Physiology Defined

Anatomy is the study of the structure of body parts and their relationship to one another. 

Physiology is the study of the function of body parts that you study in anatomy.  Examples include neurophysiology (functions the the nervous system), renal physiology (functions of the kidney), and cardiovascular physiology (functions of the heart and blood vessels)

The study of large body parts visible to the naked eye such as the heart and kidneys called  macroscopic, or gross anatomy.  Gross anatomy can be subdivided into regional anatomy, systemic anatomy,  and surface anatomy.

The study of detailed structure of body parts to small to be seen with the naked eye is called microscopic anatomy.  Examples of this would be the two subdivisions of microscopic anatomy: the study of the anatomy of the cells (cytology) and tissues (histology) forming different organs. 

The study of structural changes that occur in the body throughout the life span is called developmental anatomy. A subdivision of developmental anatomy would be embryology.



The body is arranged in the following levels of organization which are in order from the smallest and least visible  level to the largest most visible level.

1) Chemical Level: the atomic level (atoms) and the molecular level  (molecules). 

2) Cellular Level: Cells are formed from atoms and molecules forming membraneous  and non membraneous organelles which combine to form cells with specific shapes and functions in the body.

3) Tissue Level: Tissues are formed from groups of similar cells that have a common function. The four basic tissue types in the body include: epithelium, muscle, connective, and nervous tissue. 

4) Organ Level: Organs are formed from at least two or more tissues (four is most commonplace) that perform a specific function in the body.   An organ performs a specific function in the body. An example would include the stomach which contains an inner lining of connective tissue which produces digestive juices, a muscular layer below the epithelium which churns and mixes the food in the stomach, along with nerve fibers necessary for innervation of stomach muscles. 

5) Organ System Level: An organ system is formed from organs that all work together with a combined effect to perform a general function in the body.  Within each organ system there is present a division of labor among the organs in which each organ is assigned a particular task to perform to produce a particular end result. An example would be in digestion. The teeth are organs of the digestive system which digest the food mechanically by grinding the food up in the mouth, while the stomach will digest proteins, and the pancreas supplies other enzymes into the small intestine to complete the digestion of proteins, carbohydrates and fats. The organ systems include the integumentary, skeletal, muscular, cardiovascular, lymphatic, nervous, respiratory, digestive, urinary, endocrine, and reproductive systems. 

6) Organismal Level: The organism is the highest level of structural of organization and is formed from all eleven body systems working together to promote life. It is also the sum total of all the structural levels working together.


Homeostasis is the ability to maintain a "steady state" within the body of an organism, even though the external environment changes, which may bring about threatening change internally.  There are limits or ranges within which the body must be maintained internally in order to sustain life. Examples would include maintaining a constant body temperature, blood glucose levels, and the pH of the blood.


The elements of a control system include:

1) The Receptor: Control begins when a receptor detects a change in a variable in the environment called stimulus.

2) The Control Center is the second component of the control system  to which the information about the type of variable change detected by the receptor is sent. The information arrives by an afferent pathway to the control center, which contains the information on the level or range by which the stimulus is to be maintained.  An appropriate response, or course of action, is initiated by the control center  as it sends out it's appropriate response to the third element of the control system.

3) The effector is the third component of the control system.   The effector receives the information from the control center by way of an efferent pathway.  The effector then reacts appropriately by a feedback mechanism to the stimulus to return the variable back to homeostastis.   Two types of feedback mechanisms are possible: a negative feedback  mechanism which depresses or inhibits the stimulus, and a positive feedback mechanism which enhances or speeds up the reaction at an even faster rate. The most common are negative feedback mechanisms. In such a case the response of the effector would be to shut off the original stimulus, or to reduce its intensity. Negative feedback mechanisms cause the variable to change in a direction  opposite to the initial change. Our negative feedback mechanisms work very much like a home heating system. The stimulus in this case would be change in temperature. The thermostat in our house can be set to a certain temperature such as 68 degrees, and as the house warms up beyond 68 degrees it causes the thermostat (a sensor) to detect  this change. The thermostat then sends a message to a switch  to shut down the heating system (the effector) till the temperature returns to normal, at which time the heat comes back on.  This is called negative feedback because the variable is made to change in an opposite direction  to the initial change. The heat is shut off to allow the temperature the stimulus to be lowered or to move in the opposite direction.  The hypothalamus is a  biological thermostat in our brain that maintains our body temperature of 98.6 degrees F.  in much the same way.  Other examples include the withdrawal reflex, and the control of blood glucose levels by pancreatic hormones (insulin is released when sugar levels are too high and glucogon is released when sugar levels are too low).   

Positive feedback mechanisms are least common. This type of mechanism  produces a response from the control center that causes the effector to respond in such a way as to increase the level of the changing stimulus or to proceed in the same direction as the stimulus.  If our home heating system worked this way, then the temperature would continue to increase at an ever increasing rate until the house burned down.  In terms of body functions, the stimulus is influenced to completion .  Blood clotting is an example of negative feedback.  When there is a break in the skin you begin to bleed. In negative feedback steps would be taken by the control system to slow down or stop the bleeding.  Steps are taken to increase the flow of blood (not decrease the flow of blood) to the injured area. The increase in blood flow to the area will continue until completion. Completion occurs in this case when the blood clots. This is necessary because blood clotting will occur more efficiently with an increase in blood flow to the area. The excessive blood flow will also move enhance the immune process by moving disease fighting macrophages more quickly into the damaged area.  Another example of a positive feedback mechanism is the enhancement of labor  contractions during pregnancy until completion occurs, which in this case is birth.


Anatomical position refers to the body being erect (or standing up) the feet slightly spread apart, and the palms facing forward with the thumbs pointing away from the body.  The terms "right" and "left" refer to the right and left sides of the person, cadaver, or cat being viewed-not those of the observer. 




Regional terms can be applied to two fundamental divisions of the body.  The axial division makes up the main axis of the body including the head, neck, and trunk. The appendicular division includes the limbs (arms and legs) Note figure 1-7 includes the anatomical regional term and in parenthesis includes the common term.



Body planes include:

1)  Sagittal planes are vertical plans which divide the body into right and left halves. If the sagittal plane lies exactly in the midline, it is called  a median, or midsagittal plane. If they are offset from the midline they are called parasagittal planes.  

2) Frontal planes or coronal planes are vertical planes which divide the body into anterior and posterior regions.

3) Transverse, or horizontal planes divide the body into superior and inferior parts. Also called cross sections a transverse plane can exist at every possible level in the body. 

4)  Oblique sections  are cuts made diagonally between horizontal and vertical planes



Body cavities only exist within the axial portion of the body and are closed to the environment.  Two large cavities occur here called the dorsal and ventral body cavities. Each contain the internal body organs.  

The dorsal body cavity contains the brain and the spinal cord while the ventral body cavity houses the entire group of organs called the viscera, or the visceral body organs.

Other body cavities which open to the outside include the nasal cavity, the oral cavity and digestive cavity, the orbital cavities, the middle ear cavities, and the synovial cavities.


A double layered membrane called the serosa or serous membrane lines the ventral body cavity and the organs that it contains. The part of the membrane that lines the cavity walls is the parietal serosa and the layer that covers the organs in the cavity is called the Separating the serous membranes is a thin layer of lubricating fluid called serous fluid which is secreted by both membranes.  The purpose of the serous fluid to reduce friction between the organs and the body wall especially moving  organs such as the heart, lungs and the churning stomach.  The serous membranes are named for the specific cavity and organ that they cover. Examples include the parietal and visceral pericardium covering the heart and the pericardial cavity, and the parietal and visceral pleura covering the lungs and the pleural cavities, and the parietal and visceral peritoneum associated with organs in the abdominopelvic cavity.



Using two transverse planes and  two parasagital planes anatomists divide the abdominopelvic region into nine regions: 


A simpler method used by medical personnel to locate abdominopelvic organs  are quadrants in which one transverse and one median sagittal plane pass through the umbilicus at right angles. Named according the the subject's point of view they are called: the right upper quadrant (RUQ), left upper quadrant (LUQ), right lower quadrant (RLQ), and left lower quadrant (LLQ)


I) Epithelial Tissue: a sheet of cells that covers a body surface or lines a body cavity while also forming our glands.

A) General characteristics of epithelial tissue include:

1) Close-packed cells in which adjacent cells are held together by tight junctions and desmosomes

2) Epithelial cells have an apical surface (a surface exposed either to the bodies exterior, or the cavity of an internal organ), and a basal surface (an inner non exposed surface). Polarity is a characteristic of epithelial tissue meaning that the apical surface has a different structure and function than the basal surface. Cilia and microvilli for example are present on the apical surface as opposed to the basal surface.

3) A thin supporting sheet called the basal lamina found on the basal surface is a noncellular adhesive sheet consisting of glycoproteins. The basal lamina acts as a filter in that it selects which molecules can pass from the underlying connective tissue into the epithelium.

4) Below all layers of epithelial tissue is a layer of connective tissue. The reticular lamina lies below the basal lamina. The reticular lamina consists of a layer of extracellular collagen fibers which are a part of the underlying connective tissue. Together the reticular lamina and the basal lamina form the basement membrane which is found underlying all epithelial tissue. The basement membrane gives support to the epithelial tissue helping it to resist stretching and tearing.

5) Epithelial tissue is avascular (contains no blood vessels) and receive their nourishment from substances diffusing from blood vessels in the underlying connective tissue.

6) Epithelial tissue are innervated (supplied by nerve fibers).

7) Epithelial tissue constantly has to be replaced by regeneration (mitosis), because they are exposed to abrasion, acids, or bacteria. 

B) Classification of Epithelium:                                 

1)Epithelial tissue are classified as simple epithelium ( consisting of a single cell layer) in areas where absorption secretion,or filtration occur and stratified epithelium (consisting of two or more cell layers) for high abrasive areas. 

2) They are further classified according to shape as squamous cells (flattened and scalelike), cuboidal cells (boxlike-as tall as they are wide), and columnar cells (tall and column shaped

C) Simple Epithelia:

1) Simple Squamous Epithelium (figure 4.2 a) Special names given to two types of simple squamous epithelium include endothelium which provides a slick, friction reducing lining in lymphatic vessels and in all hollow organs of the cardiovascular system (blood vessels and the heart) and mesothelium which is the epithelium found in serous membranes lining the ventral cavity and its organs.


2) Simple Cuboidal Epithelium (figure 4.2.b) 


3) Simple Columnar Epithelium (figure 4.2 c) They contain microvilli on the apical surface of absorptive cells and goblet cells that secrete mucus. 


4) Pseudostratified  Columnar Epithelium (figure 4.2d) All of the cells rest on a basement membrane, but some are taller than others and when viewed from the top of the apical layer it "falsely" appears that there is more than one cell layer. 


D) Stratified Epithelium :

1) Stratified Squamous Epithelium (figure 2.4 e)  It forms the external part of the skin and extends a short distance into every body opening that is directly continuous with the skin.


2) Stratified Columnar Epithelium(figure 4.2 f) It is very rare only forming the large ducts of some glands


3) Transitional Epithelium (figure 4.2 g) Cells of the basal layer are cuboidal, or columnar and the apical cells are squamuous. The apical cells vary in appearance depending upon how much the organ which it lines is stretched.  It appears many layered when not stretched, and when stretched it thins from a six layer to a 3 layer lining. Apical cells are dome-like before stretching, and flattened and squamous like when stretched.  The "thinning" effect of this layer allows a greater volume of fluid to flow through a tube like opening, and for the storage of more fluid such as the urinary bladder.

E) Glandular Epithelium  One or more cells that secrete substances are called glands, and are formed from glandular epithelium. A secretion implies something is released by the cells that is needed by by body in contrast to excretion. Glands are classified according to whether they are endocrine glands or exocrine glands.                     

1) Endocrine glands are "ductless glands"  that secrete substances called hormones directly into the extracellular spaces.  From the extracellular fluid are carried to target organs by way of the lymphatic and circulatory systems. 

2)  Exocrine glands carry their secretions directly  onto body surfaces and into body cavities.  Unicellular glands release their secretions by exocytosis and the multicellular exocrine glands release their secretions by an epithelial lined duct. Examples include mucous, sweat, oil, and digestive glands.  The only true type of unicellular gland are goblet cells which are found between epithelial cells in the intestinal and respiratory linings. Goblet cells produce mucin which is a glycoprotein that dissolves in water as it is secreted and becomes mucus (a slimy coating that protects and lubricates surfaces). 

Multicellular exocrine glands have two basic parts: a secretory unit consisting of secretory cells (acinar cells) and a duct derived from epithelial tissue. Supportive connective tissue covers most of the glands to form a capsule around the secretory unit supplying it with blood vessels and nerve fibers. The fibrous capsule extends into the gland dividing the gland into lobes.

Structurally multicellular exocrine glands can be classified as being simple glands which have a single unbranched duct, or compound glands having a branched duct. Each of these can further be classified according to the structure of their secretory units. They are said to be tubular if the secretory units form tubes, alveolar if the secretory units form small flasklike sacs called alveoli, and tubuloalveolar if they contain both types of secretory units (figure 4.4). 

Modes of secretion is another way to classify multicellular exocrine glands.  They can be classified as merocrine glands if they secrete their products as they are being produced by exocytosis. Examples include sweat glands, the pancreas, and the salivary glands.  Another type is the holocrine glands that accumulate their products within their cells until they burst  and die. Sebaceous glands of the skin are the only true example.  They are replaced by division of underlying cells.  Another type of gland is the apocrine glands which collect cell products just beneath the free surface of the cell and instead of the whole cell rupturing, only the tip of the cell pinches off.  The cell then repairs itself and then it repeats the process as needed. The only  possible example that exists in the human is the secretion of lipid droplets by the mammary glands. Most histologists classify mammary glands as merocrine glands because of the method they use to secrete proteins.


I) Four main classes:  connective tissue proper (fat and fibrous tissue of ligaments), cartilage, bone, and blood.

II) Common properties  include 

1) A common origin (all connective tissue arises from mesenchyme (an embryonic tissue)

2) Different degrees of vascularity, or blood supply (cartilage is avascular, dense connective tissue is poorly vascularized, and others types have a rich supply of blood vessels)

3) Are composed largely of nonliving extracellular matrix separating the cells.  The matrix enables connective tissue to bear weight, and withstand great tension  that other tissues cannot.

III) Three main elements compose connective tissue: ground substance, fibers, and cells. Ground substance and fibers make up the extracellular matrix.

1) Ground substance is composed of ...

a) Interstitial (tissue)fluid

b) Cell adhesion proteins including fibronectin and laminin which serve as a connective tissue glue to attach the cells to the extracellular matrix.

c) Proteoglycans which include a protein core to which are attached glycosaminoglycans (GAGs). The GAGs which are polysaccharides which stick out from the protein like the fibers of a bottle brush. They intertwine and trap water forming a substance that varies from a fluid to a gel. The higher the GAG content, the stiffer the ground substance.

2) Fibers which give connective tissue their support are composed of three types:

a) Collagen Fibers are the strongest and most abundant and are made of the protein collagen. They are made up of tropocollagen molecules which are triple-helical secondary structures. Tropocollagen molecules then line up side by side in a staggered position to form a collagen fiber. The collagen fiber then crisscross adding even greater strength to their structure (figure2.18 page 53). The collagen fibers appear white and are called white fibers.

b) Elastic Fibers contain a rubberlike protein called elastin that allows them to stretch and recoil like rubber bands. The collagen fibers mentioned above, can only stretch so far and when the tension on the collagen fibers is removed, then the elastic fibers snap them back to their normal length and shape. Elastic fibers are found where elasticity is needed: the skin, blood vessel, and the lungs. They appear yellow and are called yellow fibers.

c) Reticular Fibers are finer collagen fibers with a different chemical structure from the collagen fibers mentioned above. They are continuous with the above collagen fibers, branching out from them and forming fine fuzzy nets.  They are found where connective tissue attaches to other tissue. An example of this would be in the basement membrane of epithelial tissue. Reticular fibers are also found around capillaries and support the soft tissue of organs.

 3) Cells forming connective tissue include a fundamental cell type which all share the suffix "blast", which means forming.  They are responsible for "forming" the ground substance and fibers characteristic of their particular matrix. They are also actively mitotic cells giving rise to other cells as they are needed.  Once they form the matrix and other cells as needed, they assume their less active mature mode and act to "maintain" the health of the matrix. At this point we add change the suffix from "blast" to "cyte" The cells include four types:

a) Fibroblasts form the connective tissue proper and change to form fibrocytes.

b) Chondroblasts form cartilage and change to form into chondrocytes. 

c) Osteoblasts form bone and change to form into osteoblasts.

d) Hematopoietic stem cells form blood and are found in our bone and are always actively mitotic (note the lack of either suffix).

e) There are other cell types that can be present besides the above four fundamental cell types listed above.  Much of our connective tissue will have nutrient storing fat cells, and mobile cells that have moved out of the circulatory system into the matrix, such as white blood cells, mast cells, macrophages, and plasma cells. The above cells are important in overall body defense against disease.

IV) Types of Connective Tissue

1) Embryonic Connective Tissue: Mesenchyme is the first tissue formed from the mesoderm germ layer in the embryo, and eventually will differentiate into all the other connective tissues (figure 4.8;page 128).  Mucous connective tissue is a temporary tissue derived from mesenchyme and similar to it. Wharton's jelly is an example and is found in the umbilical cord of the fetus. 

2) Connective Tissue Proper consist of two subclasses:

a) Loose Connective Tissue includes...

        Areolar Connective Tissue (figure 4.8 page 128) is the most widely distributed connective tissue in the body. When a body region is inflamed, the areolar tissue soaks up excess fluid and the affected area swells and becomes puffy, a condition we call edema. Because of its "loose" nature, it provides a reservoir for water and salts for the surrounding tissue.

        Adipose (fat) Connective Tissue (figure 4.8 page 129)

        Reticular Connective Tissue(figure 4.8 page 130) is like areolar tissue but only has reticular fibers in its matrix which form a network along which the reticular cells or fibroblasts are found.  Reticular fibers are widespread throughout the body, but reticular connective tissue is only found in certain places. It forms a network called a stroma which supports many blood cells (mostly lymphocytes) in the lymph nodes, the spleen and bone marrow.

b)  Dense  Connective Tissue (figure 4.8 e and f page131) includes....

        Dense Regular Connective Tissue forms our tendons and ligaments. It contains closely packed bundles of collagen fibers running in the same direction and parallel  to the direction of pull

        Dense Irregular Connective Tissue is found in areas of the body where where tension is exerted in more than one plane. The bundles of collagen fibers are thicker and run in more than one plane. It is found in the dermis, the joint capsules and the fibrous coverings around organs (testes, kidneys, bones,  cartilages, muscles and nerves) 

3) Cartilage which is avascular, and aging cartilage lose their ability to divide, cartilages heal slowly when injured.  Cartilage includes three types.....

        Hyaline Cartilage (gristle) is the most abundant body type. It covers the ends of long bones as articular cartilage, forms the tip of the nose, connects the ribs to the sternum, and forms the respiratory passageways (figure 4.8 g page 133)

        Elastic Cartilage  contains more elastin fibers  allowing it to bend more than hyaline cartilage. Forms the "skeletons" of the external ear and the epiglottis (figure 4.8 h page 133)

        Fibrocartilage forms the intervertebral discs and the spongy cartilages of the knee. It is an intermediate connective tissue and is found where hyaline cartilage meets a ligament or a tendon (figure 4.8 i page 134).

4) Bone (figure 4.8 j page 135) 

5) Blood unlike the other connective tissues does not "connect" anything. It is classified as a connective tissue, because it shares all the other characteristics of the other types of connective tissue. It develops from mesenchyme, has blood cells surrounded by a nonliving fluid matrix called the blood plasma, and the "fibers" of the blood are the protein fibers that are only visible during blood clotting (figure 4.8 page 135).

EPITHELIAL MEMBRANES consist of two tissue types: an epithelium bound to an underlying  layer of connective tissue proper. Membranes are therefore considered to be simple organs. They are composed of three types:

1) The cutaneous membrane is our skin. It consist of an outer keratinized stratified squamous epithlium called the epidermis and an inner layer of dense irregular connective tissue to which it is firmly attached called the dermis.

2) The mucous membrane or mucosae line the body cavities that open to the exterior including the hollow organs of the digestive , respiratory, and urogenital  tracts. They are all moist membranes bathed by secretions or in the case of the urinary mucosae, urine. The name of the underlying connective tissue of mucous membrane is the lamina propia, a loose connective tissue.

3) The serous membranes or serosae consist of a simple squamous epithelium (the mesothelium) resting on a thin layer of loose connective (areolar) tissue.  Fluid filtered from the capillaries is enriched with hyaluronic acid producing  the serous fluid between the parietal and visceral layers.

NERVOUS TISSUE (figure 4.10 page 137)


MUSCLE TISSUE (figure 4.11 page 138-139)